"The figure of those arrested Friday was about 1,000 in the whole country," said the official who asked not to be identified.

Many are still being held in prisons or "ghost houses", the location of which is unknown, he alleged.

"They don't tell you where they are. You are not even allowed to ask," he said.

'Rioters' blamed

Sudan's information minister called the protesters "rioters" who threaten the country's stability.

Ghazi Al-Sadiq, the minister of information, issued an appeal for people "not to allow the rioters to undermine security and stability of the Sudan".

In a statement on the official SUNA news agency, he said Sudanese have the right to peaceful expression without resorting to violence "to allow the enemies to exploit these protests to carry out foreign agendas against the country".

One of those detained is Sudanese journalist Talal Saad, who had brought some freelance photos of the protests to the AFP bureau in Khartoum on Friday.

Armed national security agents raided the bureau, ordered AFP's correspondent to delete the photos, and took Saad away. He has been unreachable for about 21 hours.

Police said in a statement that "some of the rioters" were arrested and would be brought to trial after "small groups" demonstrated in Khartoum and elsewhere.

Police contained the situation "with a minimum use of force", they said.

Witnesses said police fired tear gas and rubber bullets to disperse hundreds of peaceful protesters who had gathered in a square beside the mosque of the opposition Umma party in Khartoum.

One witness said demonstrators carried Sudanese flags and banners reading "The people want the regime to fall", a slogan used by protesters during the Arab Spring uprisings over the past year.

They burned tyres and threw stones at police before running for cover, the witness said.

Similar running battles between protesters and police took place elsewhere in Khartoum, the witness added.

International condemnations

International criticism of Sudan's crackdown increased on Friday with Canada's top diplomat expressing concern.

"We condemn the arrests of bloggers, journalists and political activists that have taken place over the last week and call for their immediate release," John Baird, Canadian foreign minister, said.

Navi Pillay, the UN High Commissioner for Human Rights, has urged the government to avoid "heavy-handed suppression" of protests and to immediately release those detained for exercising their rights to freedom of assembly and expression.

Britain and the United States have also sought the release of those detained for peaceful protest.

On June 30, 1989, Bashir seized power from democratically elected prime minister Sadiq al-Mahdi, who currently leads the Umma party.

Bashir was declared winner of a multi-party election in 2010, but observers from the European Union and the US-based Carter Centre said the ballot failed to come up to international standards.

Bashir is wanted by the International Criminal Court for crimes against humanity, war crimes and genocide allegedly committed in Sudan's western region of Darfur.

He has played down the demonstrations as small-scale and not comparable to the Arab Spring uprisings in Egypt and elsewhere, maintaining that he himself remains popular.